[DWARF] Null out the debug locs of (loop invariant) instructions hoisted by LICM in

order to avoid jumpy line tables. Calls are left alone because they may be inlined.

Differential Revision: https://reviews.llvm.org/D28390

llvm-svn: 291258

lib/Transforms/Scalar/LICM.cpp

@@ -767,6 +767,14 @@ static bool hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
   // Move the new node to the Preheader, before its terminator.
   I.moveBefore(Preheader->getTerminator());
 
+  // Do not retain debug locations when we are moving instructions to different
+  // basic blocks, because we want to avoid jumpy line tables. Calls, however,
+  // need to retain their debug locs because they may be inlined.
+  // FIXME: How do we retain source locations without causing poor debugging
+  // behavior?
+  if (!isa<CallInst>(I))
+    I.setDebugLoc(DebugLoc());
+
   if (isa<LoadInst>(I))
     ++NumMovedLoads;
   else if (isa<CallInst>(I))

test/DebugInfo/Generic/licm-hoist-debug-loc.ll

@@ -0,0 +1,75 @@
+; RUN: opt -S -licm %s | FileCheck %s
+;
+; LICM should null out debug locations when it hoists instructions out of a loop.
+;
+; Generated with
+; clang -O0 -S -emit-llvm test.cpp -g -gline-tables-only -o t.ll
+; opt -S -sroa -adce -simplifycfg -reassociate -domtree -loops \
+;     -loop-simplify -lcssa -basicaa -aa -scalar-evolution -loop-rotate t.ll > test.ll
+;
+; void bar(int *);
+; void foo(int k, int p)
+; {
+;    for (int i = 0; i < k; i++) {
+;      bar(&p + 4);
+;    }
+; }
+;
+; We make sure that the instruction that is hoisted into the preheader
+; does not have a debug location.
+; CHECK: for.body.lr.ph:
+; CHECK: getelementptr{{.*}}%p.addr, i64 4{{$}}
+; CHECK: for.body:
+;
+; ModuleID = 't.ll'
+source_filename = "test.c"
+
+; Function Attrs: nounwind sspstrong uwtable
+define void @foo(i32 %k, i32 %p) !dbg !7 {
+entry:
+  %p.addr = alloca i32, align 4
+  store i32 %p, i32* %p.addr, align 4
+  %cmp2 = icmp slt i32 0, %k, !dbg !9
+  br i1 %cmp2, label %for.body.lr.ph, label %for.end, !dbg !9
+
+for.body.lr.ph:                                   ; preds = %entry
+  br label %for.body, !dbg !9
+
+for.body:                                         ; preds = %for.body.lr.ph, %for.body
+  %i.03 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %for.body ]
+  %add.ptr = getelementptr inbounds i32, i32* %p.addr, i64 4, !dbg !11
+  call void @bar(i32* %add.ptr), !dbg !11
+  %inc = add nsw i32 %i.03, 1, !dbg !12
+  %cmp = icmp slt i32 %inc, %k, !dbg !9
+  br i1 %cmp, label %for.body, label %for.cond.for.end_crit_edge, !dbg !9, !llvm.loop !14
+
+for.cond.for.end_crit_edge:                       ; preds = %for.body
+  br label %for.end, !dbg !9
+
+for.end:                                          ; preds = %for.cond.for.end_crit_edge, %entry
+  ret void, !dbg !16
+}
+
+declare void @bar(i32*)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.9.1 (PS4 clang version 4.50.0.249 7e7cd823 checking)", isOptimized: false, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2)
+!1 = !DIFile(filename: "test.c", directory: "D:\test")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"PIC Level", i32 2}
+!6 = !{!"clang version 3.9.1 (PS4 clang version 4.50.0.249 7e7cd823 checking)"}
+!7 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 2, type: !8, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!8 = !DISubroutineType(types: !2)
+!9 = !DILocation(line: 4, scope: !10)
+!10 = !DILexicalBlockFile(scope: !7, file: !1, discriminator: 1)
+!11 = !DILocation(line: 5, scope: !7)
+!12 = !DILocation(line: 4, scope: !13)
+!13 = !DILexicalBlockFile(scope: !7, file: !1, discriminator: 2)
+!14 = distinct !{!14, !15}
+!15 = !DILocation(line: 4, scope: !7)
+!16 = !DILocation(line: 7, scope: !7)